This invention relates to a process and to a device for analysis of nonconductive surfaces --such as for example lacquers deposited on synthetic materials --by luminescent discharge spectrometry, of LDS.
The principle is already known of analysis by LDS of conductive surfaces, making it possible to have qualitative and quantitative data on the constituents of said surfaces.
The principle is based on the measurement of the luminous emission that accompanies the passage of an electric current in a gas under low pressure.
The sample to be analyzed is placed cathodically in front of an enclosure under argon, at a pressure of several mbars. The ionized argon (Ar.sup.+) under potential difference of 400.degree. to 2000.degree. dc voltage bombards the surface of the cathode sample and breaks loose the elements that constitute it. The atoms thus freed are then excited by secondary impacts with the Ar.sup.30 ions and the electrons of the plasma: while falling to a stable or less excited level, they emit a radiation whose wavelength is characteristic of the emitting atom and whose intensity is proportional to its concentration in the plasma.
The light emitted is continuously analyzed by a spectrometer.
The ion bombarding previously described leads to a plane and regular erosion, which makes possible the continuous examination of the layers deposited on the surface of a material.
However, this process of analysis is limited to samples that are conductive or of slight resistivity, to nonconductive layers of very slight thickness (less than 2 microns), and to plane samples with a diameter greater than 20 mm.